Q8.What is serialization?
Quite simply, object serialization provides a program the ability to read or write a whole object to and from a raw byte stream. It allows Java objects and primitives to be encoded into a byte stream suitable for streaming to some type of network or to a file-system, or more generally, to a transmission medium or storage facility. A seralizable object must implement the Serilizable interface. We use ObjectOutputStream to write this object to a stream and ObjectInputStream to read it from the stream
Q9.Why there are some null interface in java ? What does it mean ? Give me some null interfaces in JAVA?
Null interfaces act as markers..they just tell the compiler that the objects of this class need to be treated differently..some marker interfaces are : Serializable, Remote, Cloneable
Q10. Is synchronised a modifier?indentifier??what is it?
It's a modifier. Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
Q11.What is singleton class?where is it used?
Singleton is a design pattern meant to provide one and only one instance of an object. Other objects can get a reference to this instance through a static method (class constructor is kept private). Why do we need one? Sometimes it is necessary, and often sufficient, to create a single instance of a given class. This has advantages in memory management, and for Java, in garbage collection. Moreover, restricting the number of instances may be necessary or desirable for technological or business reasons--for example, we may only want a single instance of a pool of database connections.
Q12.What is a compilation unit?
The smallest unit of source code that can be compiled, i.e. a .java file.
Q13.Is string a wrapper class?
String is a class, but not a wrapper class. Wrapper classes like (Integer) exist for each primitive type. They can be used to convert a primitive data value into an object, and viceversa.
Q14.Why java does not have multiple inheritance?
The Java design team strove to make Java:
Simple, object oriented, and familiar
Robust and secure
Architecture neutral and portable
High performance
Interpreted, threaded, and dynamic
The reasons for omitting multiple inheritance from the Java language mostly stem from the "simple, object oriented, and familiar" goal. As a simple language, Java's creators wanted a language that most developers could grasp without extensive training. To that end, they worked to make the language as similar to C++ as possible (familiar) without carrying over C++'s unnecessary complexity (simple).
In the designers' opinion, multiple inheritance causes more problems and confusion than it solves. So they cut multiple inheritance from the language (just as they cut operator overloading). The designers' extensive C++ experience taught them that multiple inheritance just wasn't worth the headache.
Q15.Why java is not a 100% oops?
Many people say this because Java uses primitive types such as int, char, double. But then all the rest are objects. Confusing question.
Q16.What is a resource bundle?
In its simplest form, a resource bundle is represented by a text file containing keys and a text value for each key.
Q17.What is transient variable?
Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class is retrieved from the ObjectStream the value of the variable becomes null.
Q18.What is Collection API?
The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces.
Example of classes: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
Example of interfaces: Collection, Set, List and Map.
Q19.Is Iterator a Class or Interface? What is its use?
Iterator is an interface which is used to step through the elements of a Collection.
Q20.What is similarities/difference between an Abstract class and Interface?
Differences are as follows:
Interfaces provide a form of multiple inheritance. A class can extend only one other
class.
Interfaces are limited to public methods and constants with no implementation.
Abstract classes can have a partial implementation, protected parts, static methods,
etc.
A Class may implement several interfaces. But in case of abstract class, a class may extend only one abstract class.
Interfaces are slow as it requires extra indirection to to find corresponding method
in in the actual class. Abstract classes are fast.
Similarities:
Neither Abstract classes or Interface can be instantiated.
Q21.What is a transient variable?
A transient variable is a variable that may not be serialized.
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